Fault code P1111 – a step-by-step guide to diagnosing and fixing it

Error code P1111 is displayed and the check engine light is on - what does this mean?

The OBD/EOBD system has detected a manufacturer-specific DTC P1111, which relates to problems in the engine management system. This trouble code can have different meanings for different manufacturers and often relates to the fuel supply, ignition or exhaust gas recirculation. The exact definition of this fault code varies considerably depending on the vehicle manufacturer.

What causes can this fault code have?

• Defective fuel pump or insufficient fuel pressure
• Clogged fuel filter
• Damaged fuel lines or leaking connections
• Faulty ignition coils or spark plugs
• Defective mass air flow sensor (MAF sensor)
• Problems with the exhaust gas recirculation (EGR valve)
• Damaged cable connections in the engine control unit
• Defective engine control unit (ECU)
• Blocked injection nozzles
• Faulty lambda sensor

What symptoms occur in parallel with error code P1111?

• Starting problems: The vehicle is difficult to start or does not start at all
• Uneven idling: The engine runs unevenly at idle speed
• Loss of power: Significantly reduced engine power while driving
• Increased fuel consumption: Noticeably higher gasoline or diesel consumption
• Jerking when accelerating: Engine stutters or jerks under load
• Black or white smoke: Noticeable exhaust gas color from the exhaust
• Check engine light: Permanent illumination of the warning light in the dashboard

How can the problem with error code P1111 be rectified?

• Repairing this EOBD code requires a systematic diagnosis, as various components may be affected.
• Completely inspect the fuel system and replace the fuel pump and filter if the fuel pressure is below the set values
• Completely inspect the ignition system and replace defective ignition coils, ignition cables or spark plugs
• Clean the mass air flow sensor or replace with a new component if defective
• Remove EGR valve, clean thoroughly or replace if irreparably damaged
• Check all cable connections on the engine control unit for corrosion and damage and repair them
• Have injection nozzles professionally cleaned or replace if heavily soiled
• Test lambda sensors for proper function and replace if necessary
• Have the engine control unit diagnosed at a specialist workshop and replaced or reprogrammed if defective